NotTaR of small Gasoline Engines and Rotary Lawn Mowers : Engine dies or won't restart when hot   
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Engine dies or won't restart when hot

(From: Wild Bill (kwag98@tcis.net).)

There can be numerous reasons for the engine to quit running when it gets up to operating temperature.. expansion of metal parts where bolts/screws aren't tight enough, breakdown of the condenser for the ignition points (if equipped), or a possibility of a crack somewhere. An overall inspection of the tightness of fasteners would be a good place to start.

(From: Walt Conner (jerrbear@midwest.net).)

As soon as the engine shuts down, turn the flywheel by hand or DISCONNECT the plug wire and turn the blade by hand to see if there is any compression. I have had several B&S engines that did not have enough valve clearance and when hot, the valve stem expands in length enough that the valve does not properly close. After cooling, engine will be OK. Also could be a bad condenser or the other faults listed above.

(From: Michael Stevenson (mike@gi4xsf.freeserve.co.uk).)

Problems with the ignition coil can make an engine impossible to start when warm (or even stop running when it warms up), apparently this happens on motorbike engines quite often and is caused by a break in the HT coil.

A carbon track forms inside the coil where the wire is broken. When the engine is cold the carbon track has a low resistance and it conducts well enough so the spark is strong enough to start the engine, when the engine is warmer the track resistance is greater and the spark less strong. This problem gets worse over time as the carbon track gets bigger and bigger, the only remedy is to change the coil or electronic ignition module.

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